1. Field of the Invention
The present invention concerns the supply of a voltage to an electronic circuit and in particular the supply of electrical power to the electronic circuit associated with a current sensor adapted to measure the electric current flowing in a high-tension line.
2. Description of the Prior Art
A current sensor usually comprises a shunt or a torus or a Rogowski coil; the current sensor is associated with an electronic circuit producing from the analog information supplied by the sensor a (preferably digital) signal from which the current can be deduced; this signal is applied to a photodiode so that the information can be conveyed to the ground along an optical fiber. The sensor and the associated electronic circuit are at the high-tension potential; the optical fiber can provide insulation between the high-tension and the ground.
The problem arises of supplying power to the aforementioned electronic circuit; there is no question of transmitting the necessary power from the ground by means of a conventional transformer because of the high level of insulation required, which would cancel out the advantage of the envisaged measuring device.
It is therefore necessary to supply the device with power from the line current, for example using a torus provided with a magnetic core with a secondary winding supplying the necessary power supply current.
This arrangement requires a solution to a number of technical problems and an object of the present invention is to provide these solutions.
A first problem arises on the appearance of the current, especially in the presence of aperiodic components of the current: several milliseconds are required to achieve steady state conditions under which power can be supplied. The problem to be solved is that of supplying power during these few milliseconds preceding steady state conditions.
A second problem arises when high overloads occur, due to short-circuit currents caused by a fault on the line, for example: the power supply must therefore be able to withstand temporary overloads.